This invention relates to a tool and method for removing excess cement from the top of a liner after hanging and cementing thereof, a running tool including said tool, a liner-hanger system including said running tool; a casing scraper, a method of cleaning a casing using said casing scraper; an apparatus for indicating that a predetermined quantity of fluid has been ejected from a pipe in a wellbore; a liner; and a second liner hanger system.
During the construction of oil and gas wells, a wellbore is drilled in the ground a certain distance. A string of tubulars is then lowered down the wellbore and cemented in place. The wellbore is then drilled a further distance. A liner is then lowered down the wellbore and hung and cemented in place. During cementing, wet cement Is introduced through the- bottom of the liner and travels upwardly in the annular space between the liner and the wellbore. One problem which arises in the disposal of the excess cement which accumulates at the top of the liner.
Heretofore, one method of removing this cement has been by the use of a special casing scraper. Scraping of the casing with a conventional casing scraper requires a separate trip and is thus time consuming and expensive.
According to a first aspect of the invention there is provided in or for use in a running tool, a tool for removing excess cement from the top of a liner after hanging and cementing thereof.
Other features of the first aspect of the invention are set out in claims 2 to 14.
There is also provided a running tool fitted with the tool as defined above and a liner hanging system comprising a liner hanger assembly and a running tool in accordance with the present invention.
There is also provided a method for facilitating the removal of excess cement from a liner after hanging and cementing thereof, comprising the step of circulating a fluid through a stinger of a running tool and a liner.
There is further provided a method for facilitating the removal of excess cement from the top of a liner after hanging and cementing thereof, comprising the step of introducing circulating fluid in the vicinity of the top of said liner. The method is preferably carried out when the cement is wet and when the introduction of circulating fluid occurs immediately after cementing has finished and/or as soon as a packer is set in the annulus between the liner and the casing.
According to a second aspect of the invention there is provided a casing scraper comprising at least one scraper pad arranged on a tubular member, characterised in that said at least one scraper pad is rotatable about said tubular member.
Other features of the second aspect of the invention are set forth in claims 22-27.
There is also provided a method of cleaning a casing using the casing scraper in accordance with the invention comprising the steps of hanging and cementing a liner, disconnecting the running tool from the liner and raising the tool string in order to clean debris from said casing.
After the liner has been hung, the cementing procedure begins. A predetermined quantity of cement is pumped down the drill string through the tool string, through the stinger out through the bottom of the liner and up into the annulus formed by the liner and the wellbore. The cement is followed by a dart which amongst other things, cleans the interior surfaces of the drill pipe.
A problem for the well operator is that it is difficult to predict when all of the cement has left the stinger and is in the annulus between the liner and the wellbore.
Prior to this aspect of the invention, the well operator simply used a gauge which indicates the quantity of cement entering the drill pipe. This gauge can be relatively inaccurate. For example, when pumping 2000 barrels an inaccuracy of 50 barrels would not be uncommon.
When the gauge indicates that nearly all of the cement has passed the bottom of the stinger, the well operator would expect a slight pressure increase due to the dart following the cement landing in a shearable landing collar. This would be followed by a pressure drop when the shear pins joining the shearable landing collar to the stinger shear. If the dart for any reason did not land or passed through the shearable landing collar, the well operator may not realise that all of the cement in the well has passed through the end of the stinger. This could cause mud or water to be pumped into the annulus between the liner and the wellbore.
Accordingly there is provided an apparatus for indicating that a predetermined quantity of fluid has been ejected from a pipe in a wellbore, which apparatus comprises a pressure gauge, a dart comprising a body and a member shearably attached thereto, and a landing seat, the arrangement being such that, in use, said dart follows said predetermined quantity of fluid through said pipe and lands on said landing seat, a pressure increase is noted on said pressure gauge until said body of said dart shears away from said member, said pressure increase indicating that said dart has reached a known position in said wellbore.
The present invention also provides a liner having at least one of a float collar and a float shoe mounted therein, characterised in that said liner is further provided with a closure member which, in use, on withdrawal of a stinger closes, thereby allowing circulation to be carried out through the end of the stinger after withdrawal thereof, without disturbing the wet cement at the bottom of the liner and in the annulus between the liner and the wellbore.
Other features of this aspect of the invention are set out in claims 33 and 34.